package com.taobao.pojo;

import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class NtpMessage {

	/** */
	/**
	 * This is a two-bit code warning of an impending leap second to be
	 * inserted/deleted in the last minute of the current day. It''s values may
	 * be as follows:
	 * 
	 * Value Meaning ----- ------- 0 no warning 1 last minute has 61 seconds 2
	 * last minute has 59 seconds) 3 alarm condition (clock not synchronized)
	 */
	public byte leapIndicator = 0;

	/** */
	/**
	 * This value indicates the NTP/SNTP version number. The version number is 3
	 * for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI). If
	 * necessary to distinguish between IPv4, IPv6 and OSI, the encapsulating
	 * context must be inspected.
	 */
	public byte version = 3;

	/** */
	/**
	 * This value indicates the mode, with values defined as follows:
	 * 
	 * Mode Meaning ---- ------- 0 reserved 1 symmetric active 2 symmetric
	 * passive 3 client 4 server 5 broadcast 6 reserved for NTP control message
	 * 7 reserved for private use
	 * 
	 * In unicast and anycast modes, the client sets this field to 3 (client) in
	 * the request and the server sets it to 4 (server) in the reply. In
	 * multicast mode, the server sets this field to 5 (broadcast).
	 */
	public byte mode = 0;

	/** */
	/**
	 * This value indicates the stratum level of the local clock, with values
	 * defined as follows:
	 * 
	 * Stratum Meaning ---------------------------------------------- 0
	 * unspecified or unavailable 1 primary reference (e.g., radio clock) 2-15
	 * secondary reference (via NTP or SNTP) 16-255 reserved
	 */
	public short stratum = 0;

	/** */
	/**
	 * This value indicates the maximum interval between successive messages, in
	 * seconds to the nearest power of two. The values that can appear in this
	 * field presently range from 4 (16 s) to 14 (16284 s); however, most
	 * applications use only the sub-range 6 (64 s) to 10 (1024 s).
	 */
	public byte pollInterval = 0;

	/** */
	/**
	 * This value indicates the precision of the local clock, in seconds to the
	 * nearest power of two. The values that normally appear in this field range
	 * from -6 for mains-frequency clocks to -20 for microsecond clocks found in
	 * some workstations.
	 */
	public byte precision = 0;

	/** */
	/**
	 * This value indicates the total roundtrip delay to the primary reference
	 * source, in seconds. Note that this variable can take on both positive and
	 * negative values, depending on the relative time and frequency offsets.
	 * The values that normally appear in this field range from negative values
	 * of a few milliseconds to positive values of several hundred milliseconds.
	 */
	public double rootDelay = 0;

	/** */
	/**
	 * This value indicates the nominal error relative to the primary reference
	 * source, in seconds. The values that normally appear in this field range
	 * from 0 to several hundred milliseconds.
	 */
	public double rootDispersion = 0;

	/** */
	/**
	 * This is a 4-byte array identifying the particular reference source. In
	 * the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
	 * stratum-1 (primary) servers, this is a four-character ASCII string, left
	 * justified and zero padded to 32 bits. In NTP Version 3 secondary servers,
	 * this is the 32-bit IPv4 address of the reference source. In NTP Version 4
	 * secondary servers, this is the low order 32 bits of the latest transmit
	 * timestamp of the reference source. NTP primary (stratum 1) servers should
	 * set this field to a code identifying the external reference source
	 * according to the following list. If the external reference is one of
	 * those listed, the associated code should be used. Codes for sources not
	 * listed can be contrived as appropriate.
	 * 
	 * Code External Reference Source ---- ------------------------- LOCL
	 * uncalibrated local clock used as a primary reference for a subnet without
	 * external means of synchronization PPS atomic clock or other
	 * pulse-per-second source individually calibrated to national standards
	 * ACTS NIST dialup modem service USNO USNO modem service PTB PTB (Germany)
	 * modem service TDF Allouis (France) Radio 164 kHz DCF Mainflingen
	 * (Germany) Radio 77.5 kHz MSF Rugby (UK) Radio 60 kHz WWV Ft. Collins (US)
	 * Radio 2.5, 5, 10, 15, 20 MHz WWVB Boulder (US) Radio 60 kHz WWVH Kaui
	 * Hawaii (US) Radio 2.5, 5, 10, 15 MHz CHU Ottawa (Canada) Radio 3330,
	 * 7335, 14670 kHz LORC LORAN-C radionavigation system OMEG OMEGA
	 * radionavigation system GPS Global Positioning Service GOES Geostationary
	 * Orbit Environment Satellite
	 */
	public byte[] referenceIdentifier = { 0, 0, 0, 0 };

	/** */
	/**
	 * This is the time at which the local clock was last set or corrected, in
	 * seconds since 00:00 1-Jan-1900.
	 */
	public double referenceTimestamp = 0;

	/** */
	/**
	 * This is the time at which the request departed the client for the server,
	 * in seconds since 00:00 1-Jan-1900.
	 */
	public double originateTimestamp = 0;

	/** */
	/**
	 * This is the time at which the request arrived at the server, in seconds
	 * since 00:00 1-Jan-1900.
	 */
	public double receiveTimestamp = 0;

	/** */
	/**
	 * This is the time at which the reply departed the server for the client,
	 * in seconds since 00:00 1-Jan-1900.
	 */
	public double transmitTimestamp = 0;

	/** */
	/**
	 * Constructs a new NtpMessage from an array of bytes.
	 */
	public NtpMessage(byte[] array) {
		// See the packet format diagram in RFC 2030 for details
		leapIndicator = (byte) ((array[0] >> 6) & 0x3);
		version = (byte) ((array[0] >> 3) & 0x7);
		mode = (byte) (array[0] & 0x7);
		stratum = unsignedByteToShort(array[1]);
		pollInterval = array[2];
		precision = array[3];

		rootDelay = (array[4] * 256.0) + unsignedByteToShort(array[5]) + (unsignedByteToShort(array[6]) / 256.0) + (unsignedByteToShort(array[7]) / 65536.0);

		rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + unsignedByteToShort(array[9]) + (unsignedByteToShort(array[10]) / 256.0) + (unsignedByteToShort(array[11]) / 65536.0);

		referenceIdentifier[0] = array[12];
		referenceIdentifier[1] = array[13];
		referenceIdentifier[2] = array[14];
		referenceIdentifier[3] = array[15];

		referenceTimestamp = decodeTimestamp(array, 16);
		originateTimestamp = decodeTimestamp(array, 24);
		receiveTimestamp = decodeTimestamp(array, 32);
		transmitTimestamp = decodeTimestamp(array, 40);
	}

	/** */
	/**
	 * Constructs a new NtpMessage
	 */
	public NtpMessage(byte leapIndicator, byte version, byte mode, short stratum, byte pollInterval, byte precision, double rootDelay, double rootDispersion, byte[] referenceIdentifier, double referenceTimestamp, double originateTimestamp, double receiveTimestamp, double transmitTimestamp) {
		// ToDo: Validity checking
		this.leapIndicator = leapIndicator;
		this.version = version;
		this.mode = mode;
		this.stratum = stratum;
		this.pollInterval = pollInterval;
		this.precision = precision;
		this.rootDelay = rootDelay;
		this.rootDispersion = rootDispersion;
		this.referenceIdentifier = referenceIdentifier;
		this.referenceTimestamp = referenceTimestamp;
		this.originateTimestamp = originateTimestamp;
		this.receiveTimestamp = receiveTimestamp;
		this.transmitTimestamp = transmitTimestamp;
	}

	/** */
	/**
	 * Constructs a new NtpMessage in client -> server mode, and sets the
	 * transmit timestamp to the current time.
	 */
	public NtpMessage() {
		// Note that all the other member variables are already set with
		// appropriate default values.
		this.mode = 3;
		this.transmitTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0;
	}

	/** */
	/**
	 * This method constructs the data bytes of a raw NTP packet.
	 */
	public byte[] toByteArray() {
		// All bytes are automatically set to 0
		byte[] p = new byte[48];

		p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
		p[1] = (byte) stratum;
		p[2] = (byte) pollInterval;
		p[3] = (byte) precision;

		// root delay is a signed 16.16-bit FP, in Java an int is 32-bits
		int l = (int) (rootDelay * 65536.0);
		p[4] = (byte) ((l >> 24) & 0xFF);
		p[5] = (byte) ((l >> 16) & 0xFF);
		p[6] = (byte) ((l >> 8) & 0xFF);
		p[7] = (byte) (l & 0xFF);

		// root dispersion is an unsigned 16.16-bit FP, in Java there are no
		// unsigned primitive types, so we use a long which is 64-bits
		long ul = (long) (rootDispersion * 65536.0);
		p[8] = (byte) ((ul >> 24) & 0xFF);
		p[9] = (byte) ((ul >> 16) & 0xFF);
		p[10] = (byte) ((ul >> 8) & 0xFF);
		p[11] = (byte) (ul & 0xFF);

		p[12] = referenceIdentifier[0];
		p[13] = referenceIdentifier[1];
		p[14] = referenceIdentifier[2];
		p[15] = referenceIdentifier[3];

		encodeTimestamp(p, 16, referenceTimestamp);
		encodeTimestamp(p, 24, originateTimestamp);
		encodeTimestamp(p, 32, receiveTimestamp);
		encodeTimestamp(p, 40, transmitTimestamp);

		return p;
	}

	/** */
	/**
	 * Returns a string representation of a NtpMessage
	 */
	public String toString() {
		String precisionStr = new DecimalFormat("0.E0").format(Math.pow(2, precision));
		return "Leap indicator: " + leapIndicator + " " + "Version: " + version + " " + "Mode: " + mode + " " + "Stratum: " + stratum + " " + "Poll: " + pollInterval + " " + "Precision: " + precision + " (" + precisionStr + " seconds) " + "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms " + "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms " + "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + " " + "Reference timestamp: " + timestampToString(referenceTimestamp) + " " + "Originate timestamp: " + timestampToString(originateTimestamp) + " " + "Receive timestamp:   " + timestampToString(receiveTimestamp) + " " + "Transmit timestamp: " + timestampToString(transmitTimestamp);
	}

	/** */
	/**
	 * Converts an unsigned byte to a short. By default, Java assumes that a
	 * byte is signed.
	 */
	public static short unsignedByteToShort(byte b) {
		if ((b & 0x80) == 0x80)
			return (short) (128 + (b & 0x7f));
		else
			return (short) b;
	}

	/** */
	/**
	 * Will read 8 bytes of a message beginning at <code>pointer</code> and
	 * return it as a double, according to the NTP 64-bit timestamp format.
	 */
	public static double decodeTimestamp(byte[] array, int pointer) {
		double r = 0.0;

		for (int i = 0; i < 8; i++) {
			r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8);
		}

		return r;
	}

	/** */
	/**
	 * Encodes a timestamp in the specified position in the message
	 */
	public static void encodeTimestamp(byte[] array, int pointer, double timestamp) {
		// Converts a double into a 64-bit fixed point
		for (int i = 0; i < 8; i++) {
			// 2^24, 2^16, 2^8, .. 2^-32
			double base = Math.pow(2, (3 - i) * 8);

			// Capture byte value
			array[pointer + i] = (byte) (timestamp / base);

			// Subtract captured value from remaining total
			timestamp = timestamp - (double) (unsignedByteToShort(array[pointer + i]) * base);
		}

		// From RFC 2030: It is advisable to fill the non-significant
		// low order bits of the timestamp with a random, unbiased
		// bitstring, both to avoid systematic roundoff errors and as
		// a means of loop detection and replay detection.
		array[7] = (byte) (Math.random() * 255.0);
	}

	/** */
	/**
	 * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
	 * formatted date/time string.
	 */
	public static String timestampToString(double timestamp) {
		if (timestamp == 0)
			return "0";

		// timestamp is relative to 1900, utc is used by Java and is relative
		// to 1970
		double utc = timestamp - (2208988800.0);

		// milliseconds
		long ms = (long) (utc * 1000.0);

		// date/time
		String date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date(ms));

		// fraction
		double fraction = timestamp - ((long) timestamp);
		String fractionSting = new DecimalFormat(".000000").format(fraction);

		return date + fractionSting;
	}

	/** */
	/**
	 * Returns a string representation of a reference identifier according to
	 * the rules set out in RFC 2030.
	 */
	public static String referenceIdentifierToString(byte[] ref, short stratum, byte version) {
		// From the RFC 2030:
		// In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
		// or stratum-1 (primary) servers, this is a four-character ASCII
		// string, left justified and zero padded to 32 bits.
		if (stratum == 0 || stratum == 1) {
			return new String(ref);
		}

		// In NTP Version 3 secondary servers, this is the 32-bit IPv4
		// address of the reference source.
		else if (version == 3) {
			return unsignedByteToShort(ref[0]) + "." + unsignedByteToShort(ref[1]) + "." + unsignedByteToShort(ref[2]) + "." + unsignedByteToShort(ref[3]);
		}

		// In NTP Version 4 secondary servers, this is the low order 32 bits
		// of the latest transmit timestamp of the reference source.
		else if (version == 4) {
			return "" + ((unsignedByteToShort(ref[0]) / 256.0) + (unsignedByteToShort(ref[1]) / 65536.0) + (unsignedByteToShort(ref[2]) / 16777216.0) + (unsignedByteToShort(ref[3]) / 4294967296.0));
		}

		return "";
	}
}
